Integration was more "realistic" than compulsion by 2025, given a shortage of resources and teachers, he said.
National's Māori development spokesperson Nuk Korako said it was important to get children into te reo at an early age, but didn't agree with making it compulsory.
"I don't think we should be putting a patu to them saying it is compulsory. If New Zealanders want to learn it is up to them, but the opportunity should be there."
Teaching Māori history and culture would foster an interest in learning more, including te reo, he said.
"Ultimately, people need to choose to speak in their homes, communities - it has got to come from within."
ACT leader David Seymour said making te reo compulsory would "hurt New Zealand kids", who were already struggling with basic reading and writing skills.
Schools already offered the choice of te reo, he said.
Green Party co-leader Marama Davidson said simply offering the choice was not enough for the language to thrive.
"We think until the Government puts a line in the sand we won't get proper resourcing and capacity. We need to have a goal."
The New Zealand Education Institute/Te Riu Roa welcomed the Greens' push, and wanted it extended to early childhood education.
"Normalising te reo makes learning more inclusive for Māori children and must be part of our commitment to the Treaty of Waitangi," president Lynda Stuart said.
While teachers understood the importance of te reo, they often didn't feel equipped or confident to teach it effectively.
"With the current teacher shortages, overall capacity would also need to be addressed."
Several schools this week raised the issue of capacity.
Glendowie and Rosmini colleges in Auckland both said they were losing their only te reo Māori teachers at the end of the year, and were struggling to find replacements.
Te Taura Whiri (Māori Language Commission) chairperson Professor Rawinia Higgins said making te reo more noticeable was a better place to start.
"We often default to whether or not it should be compulsory, but one part is making it more visible and audible."
Television shows - including Shortland Street - mainstream media and initiatives like Mahuru Māori, which challenges participants to speak only reo through September, were increasing the amount of te reo heard in Aotearoa.
"Rather than focusing on one week a year, we should be thinking about more reo across the year."
Higgins, Victoria University of Wellington's Deputy Vice-Chancellor (Māori), said Aotearoa had come a long way.
"From the time Te Wiki started 43 years ago, when there was a generation of children where the national anthem was only in English, Māori language immersion schools were not seen as normal.
"Now we have Māori language ambassadors in mainstream media, helping shift people into a more comfortable space with te reo.
"The more we keep shifting it into an active space the easier it will come, shift the emphasis away from compulsion to usage and making it normal.
"New Zealanders don't like being told what to do, like to rebel a little bit.
"I would rather it become normal, than have to do it. English is seen as a normal subject at schools, I hope we get to that stage."
Head of Auckland University of Technology's School of Language and Culture Associate Professor Sharon Harvey said ideally New Zealand children would be learning two or even three languages at school, including te reo Māori.
"Because English is so dominant in the world, it is really important people who only speak English have the opportunity to learn another language, and get the context of a world view that is not their own.
"Māori is unique to New Zealand. There is not the opportunity to learn it anywhere else. It is a core part of citizenship."
If it became compulsory it was important culture and history were taught alongside.
"There were some major battles, major Māori leaders died in certain places - the history of the land can be accessed through English, but not the spirit."
Learning any second language had enormous benefits and made it much easier to learn other languages, Harvey said.
"The argument that Māori has no benefits outside New Zealand has no legs. It is closely linked to other Pacific languages, which is where we are located in the world.
"There are huge cognitive benefits. Monolingual speakers who have not had a good experience learning a language in school may find it more difficult as life goes on. Multilingual speakers find it much easier to pick up other languages."
